Admitting the problem is the first step- NaOH solution

[tashiany]

So, I have a problem (other than being addicted to soap making).

A few years ago I made a NaOH solution, but did not have a chance to use it. I marked it very clearly as NaOH (as one should), but did not write down its concentration.
Since then we have moved twice, and the volume changed. In addition, some white flecks appeared on the bottom.
I would hate it going down the drain (although it might do it well), and was thinking how to calculate its concentration, so to be able to use it. I have a pH meter as well as some graduated cylinders, I pulled out my old chemistry books, and looked up some YouTube videos. I was thinking of measuring the pH of a given volume and figuring out the concentration from that, but it just wouldn't make sense.

If everything else fails, I could potentially titer a small amount with acid, but if there's a better solution (hahaha) I'd rather use it.

I though that maybe someone here has encountered such a problem before, will be thankful for any assistance or ideas.

Many thanks

 

[Peachy Clean Soap]

So, I have a problem (other than being addicted to soap making).

A few years ago I made a NaOH solution, but did not have a chance to use it. I marked it very clearly as NaOH (as one should), but did not write down its concentration.
Since then we have moved twice, and the volume changed. In addition, some white flecks appeared on the bottom.
I would hate it going down the drain (although it might do it well), and was thinking how to calculate its concentration, so to be able to use it. I have a pH meter as well as some graduated cylinders, I pulled out my old chemistry books, and looked up some YouTube videos. I was thinking of measuring the pH of a given volume and figuring out the concentration from that, but it just wouldn't make sense.

If everything else fails, I could potentially titer a small amount with acid, but if there's a better solution (hahaha) I'd rather use it.

I though that maybe someone here has encountered such a problem before, will be thankful for any assistance or ideas.

Many thanks

I'm not a chemist or truly understand all the in's & out's of "Sodium Hydroxide & water amounts' I go directly to A Soap Calculator for right amounts of water & lye ratio's. You would probably like Dr. Kevin M. Dunn's Book
( Scientific Soap making ) he has lots of experiments in regards to lye' fats' & a whole lot more info. Happy Soaping, .
Update: We have a soaper here who is a "chemist" her name is @DeeAnna' she has a website called ClassicBells.com She has lots of information regarding above mentioned & much more. I reference her info a lot' its been a big help.

 

[Tara_H]

So, I have a problem (other than being addicted to soap making).

A few years ago I made a NaOH solution, but did not have a chance to use it. I marked it very clearly as NaOH (as one should), but did not write down its concentration.
Since then we have moved twice, and the volume changed. In addition, some white flecks appeared on the bottom.
I would hate it going down the drain (although it might do it well), and was thinking how to calculate its concentration, so to be able to use it. I have a pH meter as well as some graduated cylinders, I pulled out my old chemistry books, and looked up some YouTube videos. I was thinking of measuring the pH of a given volume and figuring out the concentration from that, but it just wouldn't make sense.

If everything else fails, I could potentially titer a small amount with acid, but if there's a better solution (hahaha) I'd rather use it.

I though that maybe someone here has encountered such a problem before, will be thankful for any assistance or ideas.

Many thanks

I have a similar problem, and one of these days I may get around to trying out the 'solution' (pun intended) that I tracked down. In fact I still have the tab open here: Density of aqueous solutions of inorganic sodium salts
If you have an accurate way of measuring the density it should be possible to calculate the concentration from that. In theory at least.

 

[tashiany]

We have a soaper here who is a "chemist" her name is @DeeAnna' she has a website called ClassicBells.com

Thank so you much Peachy Clean Soap, I will definitely look up both resources. I have Kevin Dunn's book, and I will also search in DeeAnnA's website. See what I can come up with...

If you have an accurate way of measuring the density it should be possible to calculate the concentration from that. In theory at least.

Tara_H, what a marvelous idea! Thank you! Where I work we have an accurate balance and a pipette, so all I need to do is take a few ml to work with me, and turn the A/C on so to have 20C (right now it's more like 32C). Will absolutely give it a try!

While writing, I also though that if I was able to somehow evaporate the water of a given volume, I can accurately weigh the leftover solid. However, that might be problematic because 1) a very concentrated solution might take a long time to evaporate, and 2) not all the mass is actually NaOH..

 

[ResolvableOwl]

@Tara_H didn't mention where she had that “density” idea from . I see one major culprit with storing lye, particularly lye solution, for a prolonged time: soda ash. NaOH is pulling carbon dioxide from the air, and forms sodium carbonate (NaOH/KOH solutions are regularly used in chemistry to remove carbon dioxide from gas streams, because they're so potent CO₂ scavengers). The well-known ash islands floating on top of an open lye pot. In small quantities, it is harmless – BUT Na₂CO₃ is a weaker base than hydroxide, and won't attack oils by its own under regular conditions, saponification will be incomplete if there is too much carbonate.

When I hear that you have made it “a few years ago”, even the smallest vent, or even diffusion through solid plastic, can be troublesome. Alarm bells: “volume changes”, “white flecks”!!!
You see in Tara_H's link that the mass densities of sodium hydroxide and carbonate are very similar, but the molar densities aren't. So a density measurement of “old” lye is unreliable at best (you don't know the ratio between hydroxide and carbonate).

I understand you don't want to toss it. You can estimate if there is a major fraction of carbonate present by acidifying some of the lye with strong vinegar/citric acid/descaler. If it fizzes, there is considerable carbonate contamination. If it only gets warm/hot, it's still mostly hydroxide. Also collect some of the “white flecks” and test them similarly (you won't want to have them in your soap anyway). Also test if they dissolve clearly in distilled water, and create turbidity when mixed with hard/tap/mineral water.

There is an old “pharmacy/lab wisdom” method of purifying lye solution from carbonate contamination: Sodium carbonate is nearly insoluble in saturated sodium hydroxide solution. Throw a ton of NaOH into the lye in question and let dissolve as much as will go into solution over days/weeks. The other advantage is that your lye atm has an unknown concentration, but when it's saturated (still solid NaOH chunks at the bottom), you can look up the concentration from the temperature (solubility limit). However, straining off the NaOH/Na₂CO₃ sediment from a roughly 50% lye is a pain not only because it's even more dangerous than typical soapmaking lye, but because you want to avoid further air contact.

 

[tashiany]

ResolvableOwl, you left me speechless!
Absolutely great!

So one option would be to go saturated- a excellent idea.

I titrated it yesterday with HCl 2M ,and got 281 gr/L. several times, so it seems accurate. Given that I usually use 2:1 water: lye solution that makes sense.
In addition, I weighed 1 ml and received 1.252 and 1.258 mg/ml, which corresponds to 25% (250 gr/L).
These are generally the same results, but not accurate enough to make soap with. But then again, the temperature might have been more than 20C..
Do you think that using a saturated solution would be a more accurate way of knowing the concentration compared to titration, or density?

 

[ResolvableOwl]

Wow! With such standards, I now feel bad for usually doing titrations only once
Have you used a pH meter, or indicator? In case of the former, was the pH change at the equivalence point suddenly, or have you seen/how have you dealt with the bicarbonate buffer knee? Did it fizz, once acidic?

Do you think that using a saturated solution would be a more accurate way of knowing the concentration compared to titration, or density?

Depends. If you are sure that you don't have considerable carbonate in there, then it's a matter of taste which one to prefer. Saturated lye solution means “incomplete masterbatch”, i. e. a bit more space for aqueous additions (goat milk, aloe vera juice, coffee etc.), but you'd always need to somehow dilute it to match concentrations of regular recipes (like your 2:1). Another advantage is that you have less chance to pull carbonate over time.
But if you want/have to get rid of carbonate, I see no alternative to saturating the solution. An alternative to adding fresh NaOH is to boil it up and let just so much water evaporate that it's a bit above saturation concentration back at room temperature. Your titration/density measurement were already a great preparation to this.